The accessibility of urban residents to green spaces is not only an essential indicator of equitable distribution of urban infrastructure but also a basic component to build livable city, which is linked with urban resident's well-being. In this study, taking Ningbo urban area as a case, we calculated the accessibility of urban green space using the Amap route planning Application Programming Interface. We also simulated the spatial distribution of urban resident based on multi-source data, including land use, nightlight, Normalized Difference Vegetation Index (NDVI), Point of Interest (POI), and road network. The spatial match between green space accessibility and urban residents' distribution was thus analyzed on the grid scale with a resolution of 100 m. Furthermore, the drivers for the accessibility of urban residents to green spaces was explored using the GeoDetector. The results show that the accessibility of green space in Ningbo is descending from each district's downtown to peripheral area, with a large proportion of poor accessibility coverage, indicating the weak green service on the whole. The area with good accessibility to green space is concentrated in the confluence of Yao River, Fenghua River and Yong River, Yinzhou new city, Beilun downtown, and Zhenhai old urban area, while the area with poor accessibility is distributed in the eastern and western mountainous area and the southern agricultural region. The accessibility of urban residents to green spaces in Ningbo shows two characteristics:high-density population and good green space accessibility in the downtown and low-density population and poor green space accessibility in the urban periphery. Also, it tends to evolve into an urban-rural dual structure at sub-district scale, which can be classified as three types including downtown, urban periphery, and industrial cluster/agricultural region/ecological conservation area. The proportion of urban residents living with green space accessibility within 15 min is less than 50%, reflecting the limited green service for urban residents in Ningbo. The drivers for the accessibility of urban residents to green spaces analyzed by the GeoDector show that five indicators as proxies for drivers are both significant. The ranking of drivers for the accessibility of urban residents to green spaces is location, human activity, development intensity, social economy, and terrain condition.